1. Field of the Invention
A certain aspect of the present invention relates to an ink cartridge and an image forming apparatus including the ink cartridge.
2. Description of the Related Art
There are image forming apparatuses (e.g., a printer, a fax machine, a copier, and a multifunction peripheral) that use a liquid-jet device to form (record or print) an image on paper (not limited to a sheet of paper but also refers to any medium on which an image can be formed, and may also be called a recording medium, recording paper, recording sheet, recording material, etc.). The liquid-jet device includes a liquid-jet head (inkjet head) as a recording head and jets a recording liquid (or ink) from the liquid-jet head onto paper being conveyed in the image forming apparatus to form an image on the paper.
In the present application, an image forming apparatus refers to an apparatus that forms an image by jetting a liquid onto a recording medium made of paper, thread, fabric, silk, leather, metal, plastic, glass, wood, ceramic, etc. Also, “image forming” indicates not only a process of forming a meaningful image such as a character or a figure on a recording medium, but also a process of forming a meaningless image such as a pattern on a recording medium. A “liquid” is not limited to a recording liquid or ink and may refer to any type of liquid capable of forming an image. Further, a liquid-jet device refers to any device that jets a liquid from its liquid-jet head.
One type of image forming apparatus employing a liquid-jet device includes a main ink cartridge (main tank or primary liquid container) with a large capacity and a head tank (sub tank or secondary liquid container) with a small capacity. The main ink cartridge is mounted on the body of the image forming apparatus and supplies ink to the head tank that is mounted on a carriage and supplies ink to a recording head. In another type of image forming apparatus, an ink cartridge used as a replaceable liquid container is mounted on a carriage together with a recording head (see, for example, Japanese Patent Application Publication No. 2006-327111 (JP2006-327111)).
Generally, an ink cartridge includes a flexible container for containing ink. Such a flexible container deforms as the contained ink is consumed and as a result, the volume of the flexible container decreases. However, the flexible container does not deform in such a manner that two opposing sides of the flexible container are kept parallel to each other and just the distance between them is decreased. Instead, the two opposing sides are unevenly deformed due to local pressures of the contained liquid. Such uneven deformation of the flexible container results in unusable ink that cannot be drawn from the ink cartridge.
When an ink cartridge becomes empty, the ink cartridge is replaced with a new ink cartridge filled with ink to continue printing. For this purpose, it is necessary to report the amount of remaining ink to the user and to request the user to replace an empty ink cartridge with a new ink cartridge.
One method of detecting the amount of remaining ink is to calculate the volume of printing (e.g., the number of printed pages), estimate the amount of used ink based on the calculated volume of printing, and calculate the amount of remaining ink based on the estimated amount of used ink. However, because of evaporation of ink and use of ink for a maintenance process, the calculated amount of remaining ink may differ from the actual amount of remaining ink in the ink cartridge. Such a difference may cause an image forming apparatus to request the user to replace an ink cartridge even when ink remains in the ink cartridge or to continue printing even when the ink cartridge is empty.
In trying to solve the above problems, JP2006-327111 proposes a method of detecting the amount of remaining ink based on the capacitance between electrodes provided on a flexible container. JP2006-327111 also discloses reinforcing parts for keeping the electrodes parallel to each other. With this method, however, the two opposing sides of the flexible container are still unevenly deformed due to local pressures of the contained liquid and it becomes difficult to accurately detect the amount of remaining ink and to correctly determine the timing to replace the ink cartridge.
Meanwhile, an ink bag used as the flexible container of an ink cartridge typically has an ink outlet for supplying ink to a recording head. The ink outlet is, for example, implemented by a rubber plug having a through hole communicating with the inside of the ink bag. An ink supply needle of the image forming apparatus is inserted into the through hole.
Ink is drawn from the ink bag via the ink supply needle by, for example, suction force produced when ink is jetted from the recording head, suction force produced by a suction pump of the image forming apparatus, or the difference in pressure head between the ink cartridge mounted on the body of the image forming apparatus and the sub tank mounted on the carriage. When ink is drawn from the ink bag to the recording head, the pressure in the ink bag decreases according to the amount of ink drawn from the ink bag and becomes negative with respect to the atmospheric pressure. If the ink cartridge is removed from the image forming apparatus when the pressure in the ink bag is negative, external air and dust flow into the ink bag through the through hole as soon as the ink supply needle is pulled out of the through hole. Also, the volume of the ink bag of a partially-used ink cartridge is smaller than original since the amount of ink has been reduced. The ink bag of such a partially-used ink cartridge tends to move in the housing of the ink cartridge when detached from or attached to the image forming apparatus and the pressure in the ink bag changes greatly. This may also cause external air and dust to flow into the ink bag. The air and dust introduced into the ink in the ink bag may in turn degrade the inkjet performance of the recording head.
Japanese Patent Application Publication No. 2006-281588 (JP2006-281588) discloses an ink cartridge including an ink bag and an ink outlet having a check valve for preventing the flow of external air and dust into the ink bag.
Also, Japanese Patent Application Publication No. 2008-134591 (JP2008-134591) discloses a configuration where reinforcing parts are provided for a flexible container to prevent uneven deformation of two opposing sides of the flexible container and to keep the two opposing sides parallel to each other.
As described above, the configuration disclosed in JP2006-327111 makes it possible to prevent remaining ink in a flexible container from becoming unusable and to relatively accurately detect the amount of remaining ink in the flexible container based on the capacitance between electrodes. However, with the disclosed configuration, it is not possible to prevent external air and dust from entering the flexible container via the ink outlet.
The configuration disclosed in Japanese Patent Application Publication No. 2006-281588 makes it possible to prevent external air and dust from entering a flexible container. However, with the disclosed configuration, it is difficult to prevent remaining ink in the flexible container from becoming unusable and to accurately detect the amount of remaining ink in the flexible container.
Meanwhile, employing both of the configurations disclosed in JP2006-327111 and JP2006-281588 increases the number of components of an ink cartridge and thereby increases the production costs of the ink cartridge.